A number of conventional techniques are available for storing data. For example, data may be stored in printed form on paper, in magnetic form on magnetic tape or floppy or hard discs, or in optical form on compact-disc read-only-memories (CD-ROM's). Of particular interest herein are optical media, such as CD-ROM's, which typically comprise discs having a diameter of 120 mm and a thickness of 1.2 mm. A spiral track is formed on the disc and includes a multitude of "pits" along the track where there is located either a nonreflective surface or a flat reflective surface portion representing the two binary states of "0" and "1" which define "bits". The bits are combined in a conventional manner to form bytes for representing data. By spacing the tracks approximately 1.6 microns apart and the pits approximately 0.834 microns apart, a CD-ROM can hold as much as 682 megabytes (MB) of data. The pits are "read" by an infrared laser having a wavelength of approximately 780-790 nanometers (nm). This technology is well known and, therefore, will not be described in further detail herein.
There are many data storage applications, such as full length video movies and libraries of books, however, which require more than 682 MB of data storage. For such applications, new techniques have been developed to pack increased numbers of pits, and hence data, onto a disc, without increasing the size of the disc. These techniques, implemented on digital versatile discs, or digital video discs (DVD) ROM's, use discs of the same physical size as CD-ROM's, but typically space the tracks 0.74 microns apart, and the pits 0.4 microns apart. The pits are read using red-laser diodes having wavelengths of approximately 635-650 nm. The pits are, additionally, formed in one or two data layers on one or two sides of the disc. By utilizing two layers of pits on each side of a disc, up to 17 gigabytes (GB, i.e., 1,000 MB) of data may be stored on a single disc, thereby providing on a single DVD-ROM about 25 times the maximum storage capacity of conventional CD-ROM's.
While the foregoing technologies enable large quantities of data to be stored on a disc by increasing the number of pits on a disc, the data represented by a single pit is still limited to a single bit. It can be appreciated that this limits not only the storage capacity of the disc, but also the rate at which data can be read from the disc. Thus, for example, if a disc has the capacity to hold 1,000 pits, then no more than 1,000 bits can be stored on the disc; furthermore, if the pits can be read a rate of 10 pits/second then data is likewise limited to being read at 10 bits/second. To circumvent the storage problems, some systems comprise multiple CD-ROM or DVD-ROM drives. Such a solution, however, is not only expensive and voluminous, but it also does not resolve the problem of the relatively limited data retrieval rates.
Therefore, what is needed is a system and method for increasing not only the data storage capacity of an optical medium, but also the rate at which the stored data may be read.